Patient-controlled analgesia (PCA) is a common and effective means of managing postoperative pain. Unfortunately, the complex processes and equipment associated with the setup, programming and administration of intravenous or epidural PCA have allowed it to become a significant source of preventable medication errors. These errors can be classified into two major categories: human (operator) errors and equipment errors (malfunctions). Such errors are potentially harmful to patients, time-consuming for hospital staff and costly for healthcare providers. The objective of this article is to describe PCA medication errors and examine systems and modalities that may help reduce the incidence of system-related errors. Data from the US FDA's Manufacturer and User Facility Device Experience (MAUDE) database indicate that 6.5% of intravenous PCA-related events were due to operator error. Most (81%) of these errors were due to pump misprogramming, of which almost half were associated with patient harm; 76.4% of adverse events were attributed to device malfunction (e.g. due to frayed wires or a crack in the drug cartridge), although only 0.5% of these were associated with harm to patients. In a report based on data from MEDMARX, a voluntary database that captures reports on medication errors, 7.9% of the PCA-related errors captured over a 5-year period were described as causing harm to patients. Technological advances, such as improved PCA pump designs based on ergonomic and cognitive engineering principles, the use of barcode technology and other 'smart pump' safety features, and new postoperative pain management modalities, may play a significant role in reducing the future incidence and severity of PCA medication errors.